[PATCH 5/6] comedi: pcmmio: validate the IRQ supplied by userspace

[Yogesh Gaur <yogeshgaur.83@gmail.com>]

comedi boards are configured through the COMEDI_DEVCONFIG ioctl, so
it->options[1] is a number chosen by userspace. pcmmio passes it to
request_irq() without checking it first, which lets an interrupt owned by
another irqdomain -- a PCI device's IO-APIC GSI, for instance -- be
claimed for this board. When the owner of that interrupt is later
released the descriptor is freed while this driver's handler is still
installed on it.

The board's interrupt is routed in software rather than jumpered, and the
driver notes that "any IRQ from 1-15 is OK", so the ISA range is exactly
the right bound.

Bound the value before requesting it, as das16m1.c already does. An
out-of-range value is ignored rather than rejected, so the board still
attaches without interrupt support, exactly as it does today when
request_irq() fails.

Fixes: 6baef150380d ("Staging: comedi: add pcmmio and pcmuio drivers")
Assisted-by: LLM
Signed-off-by: Yogesh Gaur <yogeshgaur.83@gmail.com>
---
 drivers/comedi/drivers/pcmmio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/comedi/drivers/pcmmio.c b/drivers/comedi/drivers/pcmmio.c
index f42b7343b4e4..afe2bda91659 100644
--- a/drivers/comedi/drivers/pcmmio.c
+++ b/drivers/comedi/drivers/pcmmio.c
@@ -684,7 +684,8 @@ static int pcmmio_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 
 	pcmmio_reset(dev);
 
-	if (it->options[1]) {
+	/* the irq is configured in software, so any ISA irq is OK */
+	if (it->options[1] >= 1 && it->options[1] <= 15) {
 		ret = request_irq(it->options[1], interrupt_pcmmio, 0,
 				  dev->board_name, dev);
 		if (ret == 0) {
-- 
2.55.0.windows.5